1. Field of the Invention
The present invention relates to a method for joining at least two components, which overlap at least in part, in a mechanical joining process without pre-punching, an auxiliary joining element used for this purpose, and a device for joining at least two components, which overlap at least in part, in a mechanical joining process without pre-punching according to the generic clause of claim 14.
The present invention relates in particular to a method and a device in the case of which at least two components are joined to one another under plastic deformation of said components by means of auxiliary joining elements, especially clinch rivets.
2. State of the Prior Art
In the sheet metal working industry, individual components are joined by the production methods of mechanical joining technology. The invention relates to the field of mechanical joining technology in which prepunching is not required. These low-priced methods are especially used in mass production processes in the automobile industry.
The prior art discloses methods and devices for joining overlapping, especially plateshaped components, without the process step of prepunching, the joint between the components being here established either with the aid of an auxiliary joining element, especially by means of punch riveting with a semitubular rivet or a solid rivet, or with the aid of the so-called clinching without the use of an auxiliary joining element.
In the case of these methods an overlapping area of the components is arranged between a punch and a lower die. This punch is then either pressed directly into the joining region of said two components under application of a strong force, whereby the two components undergo plastic deformation, or an auxiliary joining element is pressed into the partners to be joined with the aid of a punch. The lower die is implemented such that, when the two components undergo deformation, undercut areas are formed in the joining region between said components or between said components and the auxiliary joining element.
When an auxiliary joining element is used, said auxiliary joining element itself my be provided with undercut portions, said auxiliary joining element being then encompassed by the two components in the joining region when the components undergo plastic deformation.
In the case of these known methods, a joining force is applied by means of the punch to both components from one side, and the lower die, which is located on the opposite side, serves to take up this joining force.
In the case of variants of this method which are known as well, the linear movement of the punch is superimposed by a wobbling movement so as to reduce the joining forces and improve the flow of material, where appropriate.
In the case of the known punch-riveting process making use of a solid rivet, the auxiliary joining element is, without prepunching, pressed into the plates to be joined by means of a straight movement; in the course of this process, the opposite side is shaped by a hollow lower die and a plurality of slugs is produced as waste. The auxiliary joining element is hardened, executes the function of the cutting punch during cutting and is not deformed in the joining process.
In the case of the known wobbling punch-riveting process executed with a semitubular rivet (DE 199 27 103), the auxiliary joining element is pressed into the plates to be joined with a straight and wobbling movement, without prepunching; in the course of this process, the opposite side is shaped by a lower die and no waste is produced. The auxiliary joining element undergoes deformation during the joining process, whereby an undercut is formed.
In the case of the known wobble clinching process (DE 199 45 743), an undercut is formed in the plates to be joined, said undercut being formed, without prepunching, by means of the punch executing a straight and wobbling movement; in the course of this process, the opposite side is shaped by a lower die and no waste is produced.
In the case of the known tox clinching process (DE 199 13 695), an auxiliary joining element is pressed into the plates to be joined with a straight movement and without prepunching; in the course of this process, the opposite side is shaped by a lower die and no waste is produced.
These methods can be used when both sides of the components to be joined are accessible so that both the punch and the lower die can be arranged appropriately. Since the punch must be in alignment with the lower die, so-called C-shaped bows are used as tool frames for positioning the punch and the lower die relative to one another.
All the above-mentioned methods have the disadvantage of low coaxial tolerance. The lower die and the punch or the lower die and the auxiliary joining element must be positioned relative to one another with high accuracy so as to produce a joint of sufficient quality.
For the above-described method of punch riveting with a solid rivet, strong forces are required. These strong joining forces entail high requirements as far as the guiding of the tools is concerned. These high stresses on the tools and on the tool frames restrict the use of this method for high-strength plates. Moreover, they limit the outreach for the C-shaped bows, which are predominantly used as a tool frame, and this leads to a restriction of the applicability of the method.
Furthermore, punch riveting processes making use of a solid rivet have great disadvantages, firstly insofar as waste in the form of a plurality of slugs per joint is produced, said waste impairing the process security of the subsequent processing steps, and, secondly, insofar as the plates located on the side of the lower die get often jammed on the lower die thus causing wear and breakage of the lower die, and, thirdly, insofar as the auxiliary joining element is complicated and expensive to produce.
Also tox rivet clinching processes necessitate the application of high forces.
Both the punch riveting process making use of solid rivets or semitubular rivets and the tox rivet clinching process are additionally disadvantageous insofar as far-reaching coaxiality demands between the punch and the lower die have to be fulfilled and insofar as it is necessary to sort the auxiliary joining elements with respect to upper and lower sides, i.e. it is necessary to realize a complicated auxiliary joining element supply.
A further method has been suggested in DE 101 02 712. In the case of this method, the partners to be joined are joined by means of rivets which have a high hardness and which do not undergo a substantial deformation in the course of this process. This method does not necessitate the use of a patterned lower die. A flat anvil used as a countertool suffices for producing high-quality joints.
When this method is used, problems may arise due to the fact that the rivets are susceptible to cracking in view of the high hardness and due to cavities on the circumferential surface of the rivet, said cavities having a negative effect on the strength of the joint in the case of contact with corrosive media.
Another disadvantage is that, in the case of rivets which do not undergo substantial deformation, the residual thickness of the lowermost sheet metal layer is markedly reduced and is then often thinner than a critical value of 0.3 mm.